This invention relates generally to electric paper and gyricon displays and more particularly concerns an additive color gyricon display in which the individual color elements for providing additive color need not be aligned with respect to each other or with respect to an addressing system.
Additive color display systems are well known and many examples of them exist. For instance, televisions and CRT displays typically use additive color systems. The commonality between different additive color displays is that they all use at least the three elements of red, blue and green to provide a nearly full color gamut. White may be provided by the additive color mixing of red, blue and green and black may be provided by the inclusion of a black background matrix or by other means.
Many different arrangements of the red, blue, and green elements exist. Some minimal combination of the elements forms a pixel, with each individual color element forming a subpixel. In all cases the subpixels must each be independently addressable to allow them to be turned on or off as needed to create desired colors.
Gyricon technology was first developed over twenty years ago. Gyricon displays have numerous advantages over conventional electrically addressable visual displays, such as LCD and CRT displays. In particular, gyricon displays are suitable for viewing in ambient light, retain an image indefinitely in the absence of an applied electric field, and can be made lightweight, flexible, foldable, and with many other familiar and useful characteristics of ordinary writing paper. Thus, at least in principle, they are suitable both for display applications and for so-called electric paper or interactive paper applications, in which they serve as an electrically addressable, reusable (and thus environmentally friendly) substitute for ordinary paper. For further advantages of the gyricon, see U.S. Pat. No. 5,389,945, by Sheridon, issued Feb. 14.sup.th, 1995 titled "Writing System Including Paper-Like Digitally Addressed Media And Addressing Device Therefor" incorporated by reference hereinabove.
U.S. Pat. No. 4,143,103, by Sheridon, titled "Method Of Making A Twisting Ball Display", issued Feb. 10.sup.th, 1998 details how to make a black and white displayable surface using gyricon technology. More recently, U.S. Pat. No. 5,737,115, by Mackinlay et al., titled "Additive Color Tristate Light Valve Twisting Ball Display", issued Apr. 7.sup.th, 1998 and U.S. Pat. No. 5,717,514, by Sheridon, titled "Polychromal Segmented Balls For A Twisting Ball Display", issued Feb. 10.sup.th, 1998 detail color versions, and specifically additive color versions of gyricon displays.
Additive color gyricons come in two general forms. One of these is the additive color gyricon using bi-state or tri-state light valves. This is a gyricon in which the spheres themselves have no chromatically colored segments but which can be used to provide a full-color, red-green-blue (RGB) display. Two approaches to such a display have been described. In both approaches, the spheres in the gyricon sheet act as light valves, in that they can be used to reveal or obscure color dots to or from an observer. The spheres can be rotated through a continuous range of angles, thus allowing a continuous range of color saturation. Each of the dots can be red, green, or blue, and can be formed using, for example, an active light source, a backlit colored filter or transparency, or a reflective colored backing attached to the gyricon sheet and illuminated by ambient light. Thus the gyricon can be adapted for use in a backlit or projective mode or in ambient light.
Construction of this gyricon requires the precise placement and alignment of spheres with the colored dots and also with the mechanism for addressing the spheres. If strict alignment tolerances between the colored dots, the light valve elements and the addressing mechanism are not maintained the system will function incorrectly as the wrong colored dots are shown or obscured.
The second class of additive color gyricon is a full color additive color gyricon which uses spherical rotating elements each of which has clear outer segments and a thin colored central segment. The colored central segment of an individual spherical rotating element can be colored either red, blue or green. When a sphere is positioned such that the central segment appears edge on to an observer, the sphere will appear essentially transparent. When the sphere is then rotated 90 degrees, the colored central segment will essentially fill the field of view with its color.
Construction of this class of gyricon requires that three sets of spheres, one set having red central segments, one set having blue central segments, and one set having green central segments, be precisely placed within a gyricon sheet. Furthermore, the spheres must then be precisely aligned with the addressing electronics. Again, if strict alignment tolerances between the colored elements and the addressing mechanism are not maintained the system will function incorrectly as the wrong colors are provided.
The need for precise placement of individual elements and strict alignment between the elements and the addressing mechanism contribute to the cost and complexity of manufacturing additive color gyricons. It would be greatly desirable if an additive color gyricon could be manufactured that required neither the precise placement of individual elements nor the strict alignment tolerances between elements and the addressing mechanism.